This invention relates to a mechanical actuation system and particularly to one adapted to send high intensity mechanical shock loads to heat exchange surfaces to remove ash encrustations from the heat exchange surfaces.
Heat exchangers used by public utilities and industry are often fired by ash producing fuels. The internal surfaces of the heat exchanger often become fouled with ash encrustation during use. Such fouling adversely affects the heat transfer efficiency of the heat exchanger. Accordingly, it is necessary to provide a system for cleaning the heat exchanger surface.
One system presently in widespread use for deslagging heat exchanger surfaces are so-called sootblowers. These devices have a lance tube with a nozzle at its outer end which projects a fluid medium such as water, steam or air against the fouled surfaces. The thermal shock and mechanical impact caused by the blowing medium break away the slag encrustations from the heat exchanger surfaces. Although sootblowers generally operate satisfactorily and are superior devices in many applications, they have certain limitations. Sootblowers consume a substantial amount of blowing medium which is a direct expense to the operator of the heat exchange facility. Additionally, sootbloweres are unable to reach the areas of the heat exchanger which are inaccessible or beyond the effective range of the discharged blowing medium.
Another method for removing encrustations from heat exchanger surfaces is through the use of mechanical rappers. Conventional rappers have an impactor which through some mechanical linkage strikes a surface within the heat exchanger in order to produce a mechanical vibration which may cause the ash encrustation to disintegrate or loosen its adhesion to the heat exchanger surface.
The higher the acceleration of the structure caused by the rapper, the greater the forces imposed on the slag attached to the structure, causing it to break away. The impulse force versus time history, the locations of the structure which are driven, and the mechanical characteristics of the structure determine the mode of vibration of the structure. Rappers employing direct mechanical impact possess a number of shortcomings. These systems typically cannot be modified to deliver different pulse characteristics to produce the desired mode of resonant vibration in the surface being treated. Existing mechanical rappers further tend to be complicated in construction and may require multiple sources of power. Moreover, direct mechanical impact causes undesirable point loading on the heat exchanger structure and the rapper itself which can lead to structural failure of either.